docs: def ffmpeg_has_loudnorm():
      """
      Run feature detection on ffmpeg, returns True if ffmpeg supports
      the loudnorm filter
      """
      cmd_runner = CommandRunner([get_ffmpeg_exe(), '-filters'])
      cmd_runner.run_command()
      output = cmd_runner.get_output()
      if 'loudnorm' in output:
          return True
      else:
          logger.warning(
              "Your ffmpeg version does not support the 'loudnorm' filter. "
              "Please make sure you are running ffmpeg v3.1 or above."
          )
          return False